Amplifier with pulsating bias



June 6, 1950 D. l.. MARKUSEN 2,510,707

AMPLIFIER WITH PULSATING BIAS Filed oct. 2a, 1944 Patented June 6, 17950 "'AMPLFIERWITH TULS'G BIAS i David L2 Markursem Los Angeles, Calif; assigner t tcM-inneapolisLHoneyWell Regulator Company, Minneapolis,- Minn., a corporationof Delaware `-'Application' October 28, 1'1944`gf'Seral iNo;5560,?"798 Wide an=-elctron amplifier of extreme sensitivityV ein 'Wh-ich"l the 'effectof a signal voltage is period- "ically `changed in amplitude "by an electronic arrangement.

. f A* still furtherfobj'ect of the 'present invention istofprovde lsuch a system in which the Vsignal @voltage is a cyclically varying voltage su'chas an .-'lflternating one.

A-'ffurther object of the invention is to provide such a system in which the periodic'cha'nge in Frifmagnitude 'of Ythe` signal voltage is controlled by 1Wan" electronic `'timing arrangement.

f-A'-stll"further object oi the present `invention "Ifisf tofprovide such an arrangement -inconnection "fwith a system Yin which there'A are twooutput'dis- `charge devices, one vor theotlierof' which isl se-.-

selectively energizedfin accordance v'vth thephase relation ofvthe signal voltage with respectk to a @standard voltage.

1?- A further* object 01? the "'present' invention' is Z-ltof-provide; in connection with asy'stem such as 'f -setf 'out Iin thelast'object, means toY suppress `sigrals tending 'to' travel longitudinally'through the risystem'A to iaff'ect'undesirably both discharge Ade- `Avices'eqmally.

@ther'objectso theinvention will beapparent `rlfzom a consideration of the accompanying speci# F--T1ication;claims`, and drawing-of which Theisingle'fgure is a schematicview of my inventionappli'ed to a motorlcontrol` system.

Referring to Figure 1 of the drawing, the motor forming a part of the motor means to be controlled s-indicated by the reference numeral l I9. This f motor may be of any conventional form of-di- *rect current motor which continually rotates in 'fone' 'direction upon a direct current being passed therethrough. The motor is connected 'by conductors IIand I2 to a battery` I3 or te anyother suitable source -of unidirectional voltage. The i3' motor I0' is designed lto form the driving 'unit of a servo motor assembly having a reduction gear,

4vtrain'and vclutches for causing adrven" shaft to 4be'driven in one direction or the other. l 'For pur- Iilposes of simplification, the mechanism including 'the gearltrain and clutches has not been shown but is merely designated inV its entirety by-Vthef "''reference numeral III. The clutches are vin the .7T-form of a pair of electromagnetic clutches, one fforf the other of Whichis energized. 'The elec- E-ltroniagnetic windings of these clutches'aredes- 'iignafed-'inthe drawingiby the'reference` con-.-

fr Y suitable source' of power.

'nectio'ns` I5 and U4I 6. hen Winding -I 5 f is ener- -gizedgfionefc1utchis "engaged and the-motor is effective 'tofrrotate' ashaft II 'in one direction. ff-When "electromagnetic winding I 6' is energized, 5-fon thef'other hand,'the other'clutch is engaged andV the-shaft Il is' rotated :in theopposite direc- .'ftion. Thev motor Il) Vand theas'sembly I4 together constitute a' motor means 4functioning to provide E'reversible*motor action. f -Anyoth'er suitable" re- 1-10"versible motor couldfbe' employed.

The-"shaft 'Iiis' connectedto a suitable con- 'trc'lleddevicefl Swhich illustratively might be the 'u'.operating* mechanism "for anairplanel rudder. f y'The'S-haitfII isfa'lso connected'to a slidable conltact'larmSIS'cfa/potentiometer 2B. The contact 'r arm -cI 9V is adapted: slidably y to engage resistance A7element 2 I.

The current flow throughelectromagnetic-Wind- -''ngs fI5= and-l6 isfcontrolledv by a pair of *elecft-ronic discharge tubes23`and^2lll. In lthe -par ticularzapplica'tionwhich I- contemplate, I rhave `4l`foundx t1de'sirab1e' to rvemploy gas yilled` tubes. ""'While'the amplier isrprimarily adapted for use A='Withf-suchf'tubes, -it is to v.be understoodA that the invention-isnot -necessarily solimited. Y The tube `-23 comprises an' indirectlyA heatedcathode `25,4 a *control grid-26,and an anode 27. V.Associated -with #the fcathodeis a cathode heater 28- Whichfis connectedthrough means -(not shown) to any Thetube 24 comprises uff 'an-'idireetlyvheated cathode 29 having aheater w30, acontrolgridf3 I; and an Aanode 32. i Whilethe @tubes-.23 `auditmay-be of any suitable gas iiflled iltype, I have found -theftype '2050 gas ifilled-tube y Q iparticularly sutableviort this4 purpose. This tufbe has aishield grid r'but-*for 'purposes of simplifica- =tion,1the-shieldgrid has' been --Vomittedin the fdrawing. In use "in my circuit, thisY shield grid 'would be-` connected directly. ltothe cathode 40 f The operation l-of the..tubes -2? and `24 is controlled-by an'A impedance bridge including the .hpotentiometer 29, previously described,-l and a i control potentiometer 38. l This control vpotenti- :ometer comprises a resistor`39and a` slidable contact 4D. -The slidable contactliA is adapted'to be .-positioned byany suitableA controllerfII to which -it.is-connected by ya-link`42. "The controller '.mayll-ustratively be the gyroscope in anaircraft -for'controlling the position of the rudder in order tokeep-f the aircraft-enithc'course for which the gyroscope is set.- The right hande end fof resistor f39-is1cennected to the right hand endy of` resistor f 4r2I -by-fcenductors 243 and-44. The left handend eofresistor=39- is vconnected tcthe-lef-thand end fofY'resistorfI by conductors 4 I54 and-4 1.

Power is supplied to the impedance bridge and to the tubes 23 and 24 by a transformer '50. This transformer comprises a primary winding 5|, a high voltage secondary winding 52, and a low voltage secondary winding 53. The primary winding 5| is connected to any suitable source of alternating power of the desired frequency. The secondary winding 53 is connected by conductors 55 and' 56 to the junctions of conductors 43 and 44 and 46 and 41, respectively. The last named junctions constitute the input terminals of thel bridge while the sliders 19 and 40 constitute the output terminals of the bridge.

The output voltage of the bridge is impressed upon the primary of a coupling transformer 60. This transformer comprises a primary 6| having a grounded center tap 62 and a secondary winding 64 having a center tap 65. The slider 40 of the bridge is connected by conductor 61 to the upper terminal of primary winding 6| while the slider I9 is connected by conductor 68 to the lower terminal of primary 6|. The upper terminal of secondary 64 is connected through conductor 69, resistor 19 and conductor 1| to grid 26 of tube 23. The lower terminal of secondary 64 is connec'ted by conductor 12, resistor 13, and conductor 14 to grid 3| of tube 24. The two cathodes '25 and 29 are connected together by conductors 16 and 11, the junction of these conductors being connected to ground at 18. A condenser 19 is connected between grid 26 and cathode 25 by conductors 1|, 8|, and 16. A condenser 80 is connected between grid 3| and cathode 29 by conductors 14, 8|, and 11. The biasing means for the grids is connected between the center tap 65 of secondary winding 64 and conductor 8| leading to the two cathodes 25 and 29. The biasing means will now be described.

The biasing means comprises two different portions, one for providing a steady bias and the other for providing a pulsing voltage during certain cycles of the signal voltage. The means for providing a steady voltage comprises a battery 82 connected to a group of parallel potentiometers 83, 84, and 85. The three potentiometers are provided for simultaneously biasing several amplier circuits as will be more thoroughly described later. The potentiometer 85 is the one associated with the particular amplifier being considered and comprises a resistor 86 and a slider 81. The potentiometers 83 and 84 comprise resistors 89 and 90 and sliders 9| and 92, respectively. The three resistors 89, 90, and 86 of the potentiometers are connected together by conductors 94, 95, 96, and 91. The junction of conductors 94 and 95 is connected by conductor 98, resistor 99, and conductor to the negative terminal of the battery 82. The junction of conductors 96 and 91 is connected by conductors |02 and |03 to ground at |04 and by conductors |02 and |05, resistor |06 and conductor |01 to the positive terminal of battery 82. Thus, the resistors 86, 89, and 90 are connected across the terminals of battery 82 with the upper terminals negative with respect to the lower terminals.

Each of the sliders 9|, 92, and 81 is connected to one terminal of a further potentiometer, these further potentiometers being indicated by the reference numerals ||0, and ||2. The potentiometer ||0 comprises a resistor ||3 and a slider ||4. The potentiometer comprises a resistor and a slider H6. The potentiometer ||2 consists of a resistor ||1 and a slider ||8. Again, the three potentiometers are to provide for supplying biasing voltages to three dierent amplifiers, only one of which is shown in the drawing. The taps 9|, 92, and 81 of potentiometers 83, 84, and 8-5 are connected to the lower terminals of resistors H3, ||5, and ||1 by conductors |2|, |22, and |23, all respectively. The upper terminals of the three resistors ||3, ||5, and ||1 are connected together by conductors |24 and |25, and are connected to one terminal of a variable resistor |28. The opposite terminal of the variable resistor |28 is connected through a conductor |29 to the cathode of an electronic discharge device |3|.

The electronic discharge device 3| consists of an anode |32, a control grid |33, and a cathode |34. A resistor |35 is connected between the grid |33 and the cathode |34 by conductors |36 and |31, and a condenser |38. The junction of resistor |35 and condenser |38 is connected to ground at |39.

A condenser |4| and a resistor |42 are connected in series across the secondary 52 in a cir-l cuit extending as follows: from the upper terminal of secondary 52 through conductor |43, condenser |4|, conductors |44 and |45, resistor |92, conductor |46, ground connections |41 and |48, and conductor |49 to the other terminal oi secondary 52. The anode |32 of tube |3| is connected to the junction of conductors |44 and |45 leading to condenser |4| and resistor |42, respectively, by conductor |50. Condenser |4| and resistor |42 act to cause a shift in phase of the voltage applied to the anode |32 of tube |3|, the tube being effectively connected in parallel with the resistor |42.

While the invention is in no way limited to the use of elements having any particular value, in one particular embodiment, I found it desirable to employ condensers having a capacitance of 0.05 microfarad for condensers |4| and |38. In the same embodiment, resistor |42 had a resistance of 10,000 ohms and resistor |35 a resistance of 50,000 ohms. The variable resistor |28 had a maximum resistance of 0.5 megohm'and the resistors of potentiometers ||0, and ||2, resistances of 0.1 megohm. Each of the resistors of potentiometers 83, 84, and had a resistance ci 1,000 ohms and resistors 99 and |06 each had a. resistance of 200 ohms. The source of power available was a l0 cycle source. A type 2050 tube with its shield grid connected to the cathode was used for tube |3|. A 24 volt battery was employed for battery 82. While these values are given as illustrative, it is to be understood that other values of elements could be employed.

Operation The various elements are shown in the position that they assume when the control system is balanced. With the elements in this position, the resistance bridge consisting of potentiometers 20 and 38 is balanced by reason of sliders |9 and 40 occupying corresponding positions on their respective resistances. As a result, there is no potential dierence between sliders I9 and 40, and no voltage is supplied to the primary 6| of coupling transformer 60. This in turn results in the grids 26 and 3| being subjected only to the voltages impressed upon the tubes by means of the biasing apparatus. The operation of this portion of the system will now be described.

The grids 25 and 3| are each connected to their associated cathodes through a circuit which includes half of the secondary 64 and a path extending from the center tap 65 of secondary 64 to the junction of conductors 16 and 11 leading to the cathodes and 29, respectively, this circuit from center tap 65 being as follows.: Acenter tap 65 through conductor |55, slider I8, the lower portion of resistor I I1, conductor |23, :slider 81., the lower portion of resistor 86, conductors 91., |102, 103, vand ground connections |84 and 18 to the junction of conductors 1B and 11. It is noted that this connection includes the lower portion of resistor l I1 and the portion of resistor 8E between the slider 81 and the lower terminal 'of resistor 86. .As previously noted, the battery 82 is connected across resistor 86 so that there exists between the slider 81 and the lower terminal of resistor 86 a voltage corresponding to the ,position of slider 81. Furthermore, since thenegative terminal of battery 82 is connected t-o the upper end of resistor v8I, the slider 81 will be negative with respect to the lower terminal of :resistor l86. Since the lower terminal of the resistor is connected to the cathode and the upper terminal through resistor II1 to the grids, it will be obvious that the effect of this voltage is to bias grids 26 and 3| negatively.

As previously noted, the anode and cathode of tube I3I are connected in parallel with resistor I 42 which in turn is in a circuit including the high voltage Asecondary 52 and lcondenser IM. Consequently, the alternating voltage across resistor |42, which slightly leads in phase the voltage across secondary 52 is always impressed across the anode and cathode of tube I3I. The condenser I38, being connected between the grid and cathode, as previously explained, determines the biasing Voltage impressed upon grid '|33 and hence determines whether the tube |3| is conductive. Condenser |38 has at all times impressed on it a voltage which is dependent upon 'the position of sliders 9|, 92 and '81, beingr connected across the lower portions of the three potentiometers with which these sliders are associated. Thus, a circuit including condenser |38 vexists as follows: from the lower terminal of resistor 86 through conductors 91, IIl2 and |63, ground connections |04 and |39, condenser |38, conductor |25, resistor |28, conductor |25, resistor ||1, and conductor |23 to slider 81. Since the portion of resistor B5 between slider 81 and the lower terminal thereof has always impressed yacross it a direct current voltage, the polarity of slider 81 being negative with respect to the lower terminal of resistor 86 it will be obvious that the effect of the circuit 'just traced is to continually impress on condenser |38 a voltage tending to make the lower terminal of condenser |38 positive with respect to the upper terminal. Thus, the gri'd |33 tends to 'be maintained slightly positive with respect to cathode |34 so that as far as the effect 'of the circuits just traced are concerned, the -tube I 3| is conductive, the discharge circuit thereof being as follows: from the junction of conductors |44 and |45 through conductor |50, anode |32, cathode |34, condenser |38, and ground connections |39 and |41. As soon as tube |3I discharges through the circuit just traced, the resista-nce lof tube I3| drops to a very low value so that substantially the full voltage between the junction of conductors |44 and |45 and ground is impressed on condenser |38. The polarity of this voltage is opposite to that impressed upon it by the battery 82 land the potentiometers-33, 84, vand B5. In other words, the eiect of the discharge is to render the upper terminal -of the :condenser highly positive with respect to the lower terminal and to impose a very high-ly negative :bias on the grid |33. The "effect of this bias is -to cause the discharge to terminate :at the end of the halfcycle in which `the tube is recL Upon the occurrence of the next half cycle in which the anode 132 is positive with respect to the cathode |34, the oondenser |38 vimposes such a .highly negative voltage upon the grid .|33 that the tube 113i cannot discharge.

As soon .as condenser .|38 Abecomes :charged .in the manner just described, the charge begins to leak A oi through the following circuit: .from the upper terminal of condenser |38 through conductor |253, resistor 1:28 the three resistors H3, |15, and |I1, the lower portions of resistors 89, 93., :and 83, conductors |02 and |93., and ground connections 'I'Ill and |39 to .the lower terminal of condenser |38. The resistance :in this discharge lcircuit is suiiiciently .high that an appreciable time is required for the discharge of condenser I 38. 'The length of this time can vbe varied by varying the value of adjustable resistor |28. In o-ne preferred embodiment of my invention, I have maintained the resistors so adjusted that the tube |31 is able to discharge every other-cycle. in .some cases, however., .it is desirable to have it discharge lless frequently, Vfor example, once every four cycles.

Due to the discharge `circuit lfor condenser .|38 traced above, a portion Aof the voltage across condenser |38 is impressed across resistors |13, I5, and ||1.. It will be recalled that in the biasing circuit traced for the grids .26 and 3=| of tubes .23 and 24, the lower portion of `resistor |I1 was included. Thus, the 'voltage impressed across the lower portion of resistor If|1 as wel-1 as across the lower portion of Yresistor 86 is :impressed upon grids 26 and 3i. However, the voltage impressed on lthe lower portions of resistors .|:I1 4and 86 by :condenser |38 raises the potentials vof slider I I8 and slider 81 in the positive direction with respect to the lower terminals of their resistors. In other words, the eiect of this voltage is opposite to that of .battery 82. Thus, during that :half cycle .in which tube 13| is discharging, the bias voltage introduced 'by battery 82 is opposed by the voltage applied -by condenser |38. By proper adjustment "of the slider I lI 8, the amount of voltage introduced by condenser .|38 can be adjusted :so that the effective negative biasing voltage applied to grids 26 and 3| will still be slightly greater than the value at which these tubes become conductive.

Now let it assumed vthat 'the condition to whichA controller 4`| 'is responsive changes so as 'to cause a movement of the slider 40 very slightly to the right. This will cause a very slight unbalance voltage'to be applied to the primary A16| Vof the coupling transformer 611. This slight iunbalance 'voltage 'will be applied to the grids 26 and 3i yinad'dition 4to the biasing voltages introduced by the biasing portion of the Vapparatus just described. The phase relation .of this unbalance voltage 'to the voltage supplied to the anodes will be dependent :upon the relation .of lwindings 52 and 53. Let it be assumed that the phase relation is such that during the half -cycle when anodes 21 and 32 are positive withirespect to cathodes 25 Land 29., the effect of the unbalance voltage is to tend .to render grid 26 positive with respect 'to cathode 25. Under these conditions, since :gri/d3] is connected to the opposite end of the Ysecondary winding '64, the eiect of the same unbalancevoltage would -he to render grid 3| .negative with respect to cathode 29 dur-ing the same cycle. Thus, 'the tendency of the imbalance voltage, assuming the conditions described, .is to render tube 2.3 conductive and to render tube 2l non-conductive. However,

the grids 26 and 3| are also subjected to the biasing voltage of the biasing portion of the appara-v tus. Now let it be assumed that the signal caused by the movement to the right of slider 48 is of such magnitude that the voltage impressed by reason of it on grid 26 is just able to raise the grid above the cut-off voltage when the biasing voltage consists not only of the component introduced by battery 82 but the opposing component introduced by reason of the discharge of tube |3|, but is insufficient to raise the grid above the cut-off voltage when the biasing voltage consists only of the component introduced by battery 82. Under these conditions, tube 23 will be conductive duringeach cycle in which tube |3| discharges, for example, every other cycle. As a result of this discharge, current will ow through clutch winding I6 as follows: from the upper terminal of secondary 52 through conductors |43 and |60, electromagnetic clutch winding I6, conductor I6I, anode 21, cathode 25, conductor 18, ground connections 18 and |48, and conductor |49 to the lower terminal of secondary 52. Thus, the effect of the unbalance signal is to cause the clutch winding I6 to be energized so as to cause rotation of shaft I1 in one direction. Since, however, the unbalance signal is very small, clutch I6 will be only energized every other cycle so that the rotation of shaft I1 will be relatively slow.

The Yeffect of rotation of shaft I1 is to cause slow movement of the controlled device. At the same time, the slider I9 is moved to the right so as to tend to cause the positions of sliders I9 and 4D to be again the same. Due to the very slight movement of slider 40 which causes the original unbalance of the bridge, only a small amount of movement of the control device and slider I9 are necessary to again rebalance the bridge. The controlled device will now be in a position corresponding to that of the controller and the balanced conditions described at the beginning of the operation will again exist.

Now let it be assumed that the condition to which the controller is responsive deviates slightly in the opposite direction so as to cause the controller to move slider 68 to the left. The unbalance voltage will now be 180 degrees displaced in phase from that previously considered so that during the half cycle in which the anodes 21 and 32 are positive with respect to cathodes 25 and 29, the effect of the unbalance voltage will be to tend to cause grid 3| to be positive `with respect to cathode 29 while the effect on grid 28 is to tend to cause it to be negative with respect to the cathode. Let it be assumed that the movement of slider 40 to the left causing this unbalance voltage is substantially the same in magnitude as the previously described movement of slider 40 to the right. The unbalance voltage hence will be substantially the same in magnitude so that again the effect of the unbalance voltage is unable to overcome the biasing effect of battery 82 alone but is able to overcome the effect of battery 82 when the latter is opposed by the voltage introduced by condenser |38.V Hence, during those half cycles in which tube |3| is discharging, the grid 3| will assume a potential suiciently high with respect to that of the cathode 29 to cause tube 24 to be conductive. The result of this will be the establishment of a circuit through clutch winding I5 as follows: from the upper terminal of secondary 52 through conductors |43 and |68, clutch winding I5, conductor |63, anode 32, cathode 29, conductor 11, ground connections 18 and |48, and conductor M9 to the lower vterminal of secondary 52.

The effect of the establishment .of the circuit just traced is to cause the clutch associated with winding I5 to be energized so as to cause shaft I1 to rotate in the direction opposite to that previously considered. This will in turn cause movement of the controlled device I8 and the slider I9 in the opposite direction, slider I9 now being moved to the left. Again, due to the slight movement of slider 48 to the left, only a slight movement of controlled device I8 and slider I9 will be necessary to rebalance the bridge and stop movement of the controlled device. Again, due to the fact that tube 24 is conductive only during certain cycles, the movement of the controlled device I8 will be very gradual.

Now let it be assumed again that the slider 40 moves to the right but that the movement is rather substantial due to a substantial change in the condition to which controller 4| is responsive. Under these conditions, the phase of the voltage will again be such as to render tube 23 conductive. The magnitude of the unbalance voltage, however, will now be sufcient to overcome the bias introduced by battery 82 even during those cycles when the tube |3| is not conductive. Thus, the tube 23 will be conductive during each half cycle so that the winding I8 is energized each cycle. The movement of shaft i1 and hence of controlled device I8 will accordingly be more rapid than before. Let it be assumed, for example, that the resistor |28 is adjusted so that tube |3| discharges every other cycle. In this case, the movement of shaft I1 will be twice as fast as when only the slight amount of unbalance of the bridge occurred. Hence, while the deviation is greater, the rate at which it is readjusted is also greater so as to cause a quick adjustment of the controlled device despite the greater deviation.

It will be obvious from the above description that if a substantial deviation of the condition occurs in the opposite direction so as to cause slider 48 to move a substantial distance to the left, the clutch winding I5 will be energized each cycle instead of each half cycle as described. Again, the movement of controlled device I8 will be at a more rapid rate.

It was noted above that the tube |3| is subjected to the voltage across resistor |42 which is slightly leading in phase to that existing across secondary 52. The reason for this is that it is desirable for the peaking voltage introduced by reason of the discharge of tube |3| and the resultant charge of condenser |38 to occur only slightly after the beginning of the positive cycle of the plate voltage, despite the delay in the build up of this voltage caused by condenser |38. Were plate |32 connected directly to the upper terminal of secondary 52, the anode |82 would become positive at the same instant as anode 32 so that by the time the condenser became charged up the peaking voltage would be impressed on the grids at the latter portion of the conductive half cycle rather than at the beginning thereof.

As previously noted, the potentiometers 83 and 84 as well as the potentiometers IIl'i and III are provided for taking care of other amplifiers. In a complex system utilizing a plurality of balanced bridges each with its own amplifier, it is undesirableto provide a separate biasing arrangement for each amplifier. By the arrangement shown in the drawing, it is possible to simultaneously supply all of the amplifiers with both a biasing voltage and a peaking voltage without any danger of signals Vbeing introduced from onev system to the other to cause undesired discharge of the highly sensitive gas filled tubes. A

The transformer 60 having a primary 6| with a Vgrounded center tap @2 performs a very desirable function in eliminating transient effects which might egually aiect grids 2B and 3 l L There is a tendency for transient voltages of a type commonly referred to as YlongitudinalsA to travel down the opposite leads to the grids o f both tubes and cause them .to discharge even though 110 Sigf nal voltage is present. These transient voltages are of relatively high frequency, being introduced through the source of power or being produced in the amplifier circuits asa result of lthe sudden discharge of the tubes, particularly tube itl. By reason of their h igh frequency, they are conducted between windings of transformer 50 by reason of the capacity eiect between the windings. Thus, if transformeril were not present, one such current Would travel frorn 'the transformer through conductor 5,5, conductor 61, conductor 69, resistor 1B, and conductor 1I, to grid 26. The other would travel through conductors 55, 68, and 12, resistor 13, and conductor 'i4 to grid 3|. The voltages associated with these currents would be in phase with each other and would under certain conditions cause simultaneous ring of the tubes. By placing the coupling transformer B into the connections and by grounding the center tap of primary 6|, this diniculty is eliminated. The current traveling down line 61, for example, will travel through the upper portion of winding Si and pass to grounded tap 62. The current traveling along vconductor 68 will pass through the lower portion of primary winding 6l to ground at 62. Since the two currents are in phase with each other, the effects of these currents on the total voltage across the primary Will be in opposition so that no effect whatsoever will be produced by them Vin the secondary 64. This feature isof particular importance in connection with an amplifier of the high sensitivity made possible by the biasing means described above in Awhich the tubes are caused to fire upon the presence of extremely slight unbalance voltages. With such a system in which a pulsing voltage is introduced during certain predetermined cycles, the eifect of transient voltages such as the longitudinale just considered is more pronounced since 4obviously such a longitudinal occurring during a cycle which the pulsing voltage is applied is much'more apt to cause the discharge of both tubes than in a more conventional type of system in which a greater signal is required to cause discharge of the tubes.

It will be seen that -I have provided an extremely sensitive amplifier in which the presence of all moving elements is entirely eliminated. While I have shown a specific embodiment of my invention for purposes of illustration, it is to be understood that the invention is to be limited only by the scope of the appended claims.

I claim as my invention:

1. In combination, a pair of electronic dis.- charge devices each having an input and an output circuit, means for applying an alternating voltage to the output circuits of both devices, means for producing an alternating signal voltage of the same phase or the opposite phase to that of the output voltage dependent upon the condition of a main controller, means for applying to the input circuits of said two tubes alternating voltages which are opposite in phase to each other but both of a phase dependent upon that of said signal voltage so ,that one or the 10 other of said dischargedevices tends to be conductive, and means including an electronic timer for applying a further biasing voltage ofthe same polarity to both of said input circuitsduring a portion of the cycles of said alternating signal voltage,

2. In combination, a pair of electronic discharge devices each having an input and an output circuit, means for applying an alternating voltage to the output circuits of both devices, means for producing an alternating signal voltage of the same phase or the opposite phase to that of the output voltage dependent upon the condition of a main controller, means including a coupling transformer for applying to the input circuits o'f said two tubes alternating voltages which are opposite in phase to each other but both of a phase dependent upon that of said signal voltage so that one or the other` of said discharge devices tends to be conductive, and means including an electronic timer for applying a further biasing voltage of the same'polarity to both of said input circuits during a portion of the cycles of said alternating signal voltage, the primary winding of said coupling transformer having a center tap connected to ground so as to balance out in said primary winding any transient .voltages existing between the terminals of said primary AWinding and ground.

3. In combination, a pair of electronic discharge devices each having an input and an output circuit, means for applying an alternating voltage to the output circuits of both devices, means for producing an alternating signal voltage of the same phase or the opposite phase to that of the output voltage dependent upon the condition of a main controller and tending to include undesirable transient voltage, and means including a coupling transformer having a primary winding connected to said signal voltage producing means and secondary winding means connected to the input circuits `of said two discharge devices for applying to the input circuits of said two discharge devices alternating voltages which are opposite in phase to each othel` but both of a phase dependent upon that of said signal voltage so that one or the other of said discharge devices tends to be conductive, the primary winding of said coupling transformer having a center tap connected to ground so as to balance out in said primary Winding any such transient voltages in said signal voltage producing means conducted to the terminals of said primary winding and applied between said terminals and ground.

4. In combination, an electronic amplifier having an input circuit and an output circuit, means including means responsive to a condition for applying a signal voltage variable in magnitude to said input circuit, the magnitude over a range of values vof said signal voltage being dependent upon the value of said condition, meansfor applying a fixed biasing voltage to said input circuit so .that Said amplier .is conductive 01115' if Said signal voltage is greater than a predetermined magnitude, and means including' an electronic Ytimer for periodically adding to said input circuit a further voltage of short'dm'a'in .tending t0 render said amplifier Yconductive butl said further voltage being of such limited magnitude as to cause said amplifier to be conductive only when the magnitude of said signal voltage is above a predetermined value lower than said first named predetermined magnitude.

` 5. In combination, an electronic amplifier having an input circuit and an output circuit, signal means adapted to be energized from an alternating source of power for applying an alternating signal voltage variable in magnitude over a range of values to said input circuit, means adapted to be energized from the same alternating source of power as said signal means for applying a further adjustable voltage to said input circuit to render said amplifier conductive only if said signal voltage is above a predetermined magnitude, and means including a condenser for periodically interrupting the application of said further voltage forr a predetermined number of cycles of said alternating signal voltage so that said amplifier is conductive during said cycles only if said signal voltage is above a second higher predetermined magnitude.

6. In combination, an electronic ampliiier having an input circuit and an output circuit, signal means adapted to be energized from an alternating source of power for applying an alternating signal voltage variable in magnitude over a range of values to said input circuit, means adapted to be energized from the same alternating source of power as said signal means for applying a further adjustable voltage to said input circuit beginning with a predetermined portion of a cycle of said alternating signal voltage to render said ampliner conductive only if said signal voltage is above a predetermined magnitude, and means including a condenser for periodically interrupting the application of said further voltage for a predetermined number of cycles of said alternating signal voltage so that said amplier is conductive during saidcycles only if said signal voltage is above a second higher predetermined magnitude.

7. In combination, an electronic discharge device of the gas lled type having an anode, a cathode, and a control element, means for applying a signal voltage of variable magnitude between said control element and cathode, means for applying a direct current biasing voltage between said control element and cathode of such magnitude as to prevent said discharge device from being conductive unless the magnitude of said signal voltage is above a lrst predetermined value, and means including an electronic timer including an impedance network for producing a voltage drop across said impedance network to produce a periodic voltage acting in opposition to said direct current biasing voltage for periodically decreasing the magnitude of said biasing voltage suflciently that said discharge device is conductive at a lower value of said signal voltage but not sufficiently to render said discharge device conductive in the absence of a signal voltage.

8. In combination, an electronic discharge device of the gas filled type having an anode, a cathode, and a control element, means for applying a signal voltage of variable magnitude between said control element and cathode, means for applying a direct current biasing voltage between said control element and cathode of such magnitude as to prevent said discharge device from being conductive unless the magnitude of said signal voltage is above a first predetermined value, and an electronic timer including an impedance network for producing a voltage drop across said impedance network to produce a periodic voltage acting in opposition to said direct current biasing voltage for periodically decreasing the magnitude of said biasing voltage sufciently that said discharge device is conductive at a lower value of said signal voltage but not s 12 sufficiently to render said discharge device conductive in the absence of a signal voltage, said impedance means including a condenser and said timer further including an electronic discharge device for periodically charging said condenser at intervals less frequent than the cycles of said signal voltage.

9. In combination, an electronic discharge device of the gas lled type having an anode, a cathode, and a control element, means for applying a voltage between said anode and cathode, means for applying a signal voltage of variable magnitude between said control element and cathode, means for applying a biasing voltage between said control element and cathode of such magnitude as to prevent said discharge device from being conductive unless the magnitude of said signal voltage is above a rst predetermined value, and means including an electronic timer for periodically decreasing the magnitude of said biasing voltage suiciently that said discharge device is conductive at a lower value of said signal voltage but not sufciently to render said discharge device conductive in the absence of a signal voltage, said electronic timer comprising a condenser and an electronic discharge device having a cathode circuit, which includes said condenser, and having an input circuit and an output circuit both of which are common to said cathode circuit and said condenser, said discharge device being operative to periodically charge said condenser at intervals dependent upon the rate of discharge of said condenser.

10. In combination, an electronic discharge device having an anode, a cathode, and a' control element, means for applying a signal voltage variable in magnitude between said control element and cathode, means including a resistor for applying a direct current biasing voltage between said control element and cathode tending to render said discharge device non-conductive except when the magnitude of said signal voltage is above a rst predetermined magnitude, and means including an electronic timer including an impedance network for producing a voltage drop across said impedance network to produce a periodic voltage acting in opposition to said direct current biasing voltage for periodically applying a further direct current voltage in opposition to said biasing voltage to decrease the magnitude of signal voltage "necessary to cause the discharge device to be conductive.

11. In combination, an electronic discharge device have an anode, a cathode, and a control element, means for applying a voltage between said anode and cathode, means for applying a signal voltage variable in magnitude between said control element and cathode, means including a resistor for applying a biasing voltage between said control element and cathode tending to render said discharge device non-conductive except when the magnitude of said signal voltage is above a rst predetermined magnitude, and an electronic timer for periodically applying a voltage in opposition to said biasing voltage to decrease the magnitude of signal voltage necessary to cause the discharge device to be conductive, said electronic timer including a condenser, an electronic discharge device having a cathode circuit including said condenser for charging said condenser at intervals whose length is determined by the rate of discharge of said condenser, and a discharge circuit for said condenser' including said resistor of said biasing means.

12. In combination, an electronic discharge deandro? 'vice having an anode, a cathode, and a control element, means for applying a voltage between said anode and cathode, means for Aapplying a signal voltage variable in magnitude between said control element vand cathode, means including a resistor for applying a biasing voltage between .said control element and cathode tending to render said discharge device non-conductive except when the magnitude of said signal voltage is above a first predetermined magnitude, and an electronic timer for periodically applying a Voltage in opposition to said biasing voltage to decrease the magnitude of signal voltage necessary to cause the discharge device to be conductive, said electronic timer including a condenser, an electronic discharge device having a cathode circuit including said condenser for charging said condenser at intervals whose length is determined by the rate of discharge of said condenser, and a discharge circuit for said condenser including said resistor of said biasing means and a variable resistor for varying the discharge rate of the condenser.

13. InA combination, an electronic discharge device of the gas filled type having an anode, a cathode, and a control element, means for applying a voltage between said anode and cathode, means for applying a signal voltage of variable magnitude between said control element and cathode, means for applying a biasing voltage between said control element and said cathode of such magnitude as to prevent said discharge device from being conductive unless the magnitude of said signal voltage is above a first predetermined value, and timing means for periodically modifying the magnitude of said biasing voltage so as to require a different value of said signal voltage for said discharge device to be conductive, said timer means including a condenser, and a gas filled electronic discharge device having a cathode circuit including said condenser, said gas lled electronic discharge device controlled by the charge on said condenser for charging said condenser at intervals dependent upon the discharge rate of said condenser.

14. In combination, an electronic amplier having an input circuit and an output circuit, means adapted to be energized from a source of cyclically varying power for applying a cyclically varying voltage to said output circuit, means adapted to be energized from the same source of cyclically varying power for applying to said input circuit a cyclically varying signal voltage variable in magnitude and related in phase to the voltage applied to said output circuit, a source of biasing voltage, means connecting said biasing voltage to said input circuit, and means including an electron discharge device and an impedance network for producing a voltage drop across said impedance network to produce a voltage acting in opposition to said biasing voltage for abruptly adding to said biasing voltage a further voltage to change biasing effect of said biasing means on said input circuit sufiiciently that said amplier will be operative for over only a variable number of its operating cycles when said signal voltage is in one range of values and to be ineffective to maintain said amplifier operative or inoperative when said signal voltage is respectively greater than or less than said one range of values.

15. In combination, an electronic discharge device of the gas filled type having an anode, a cathode, and a control element, means for applying a signal voltage of variable magnitude between said control elementland cathode, a cyclically varying power supply, means .operatively `connecting said power supply to said anode and cathode, means for applying a biasing voltage betweensaid control element and cathode of such magnitude as to prevent said discharge device from being conductive unless the magnitude of said signal voltage is above a rst predetermined value, and `means including an electronic timer including Van impedance network for producing a voltage drop across said impedance network to produce a periodic voltage acting in opposition to said biasing voltage for periodically abruptly adding to said biasing voltage a further voltage to change the biasing effect of said biasing means sufficiently that said discharge device will be rendered conductive over only a variable number of its operating cycles when said 'signal voltage varies between said first predetermined value and a second predetermined value below said first predetermined value and said discharge device will remain inoperative when said signal voltage is below said second predetermined value.

16. In combination: an electronic amplifier having an input circuit and an output circuit; means adapted to be energized from a source of cyclically varying power for applying a cyclically varying voltage to said output circuit; means adapted to be energized from the same source of cyclically varying power for applying to said input circuit a cyclically varying signal voltage variable in magnitude and related in phase to the voltage applied to said output circuit, said signal voltage being effective when above a predetermined magnitude to cause said amplier to be conductive; a source of direct current biasing Voltage; means connecting said biasing voltage to said input circuit; an impedance network; and means including an electronic discharge device adapted to be energized from the same source of cyclically varying power as said previously named means and effective when so energized to produce a voltage drop across said impedance network to produce a periodic voltage to modify said direct current biasing voltage on said input circuit during a predetermined portion of the cycles of said signal voltage, said modified direct current biasing voltage being of such character as to tend to render said amplifier conductive but of such limited magnitude that said amplier is conductive only in the event of a signal voltage of a magnitude above a predetermined value which is lower than said first named predetermined magnitude.

1'7. In combination: an electronic discharge device of the gas filled type having an anode, a cathode, and a control element; means for applying a cyclically varying voltage between the anode and cathode of said device; means for applying between the control element and cathode a cyclically varying signal voltage variable in magnitude and related in phase to the previously named voltage, said signal voltage being effective when above a predetermined magnitude to cause said discharge device to be conductive; a source of direct current biasing voltage; means connecting said biasing voltage between said control element and said cathode; and means including an electronic timer including an impedance network to produce a voltage drop thereacross to produce a periodic voltage for modifying said direct current biasing voltage for a time period of short duration during certain of the cycles of said signal voltage, said modified direct current biasing voltage being of such character as to tend to render said discharge device conductive but of such limited magnitude that said device is conductive only in the event of a signal voltage of a magnitude above a predetermined value which is lower than said first named predetermined magnitude.

18. In combination: an electronic discharg device of the gas filled type having an anode, a cathode, and a control element; means for applying a cyclically varying voltage between the anode and cathode of said device; means for applying between the control element and cathode a cyclically varying signal voltage variable in magnitude and related in phase to the previously named voltage, said signal voltage being effective when above a predetermined magnitude to cause said discharge device to be conductive; a source of direct current biasing voltage; means connecting said biasing voltage between said control element and said cathode; and means including an electronic timer including impedance network for producing a voltage drop across said impedance network to produce a periodic voltage `for modifying said direct current biasing voltage for a timevperiod of short duration during certain of REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,938,742 Demaresi'l Dec. 12,` 1933 2,026,308 Ganz Dec. 31, 1935 2,190,514 Garman Feb. 13, 1940 2,253,129 Lord Aug. 19, 1941 2,332,325 Levoy, Jr Oct. 19, 1943 Certificate of Correction Patent No. 2,510,707 June 6, 1950 DAVID L. MARKUSEN It is hereby certified that error appears in the printed speeication of the above numbered patent requiring correction as follows:

Column 2, line 31, for idireetly read indirectly; column 10, lines 60 and 61, strike out over a range of values and insert the same in line 59, after the Word magnitude and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 31st day of October, A. D. 1950.

[SEAL] THOMAS F. MURPHY,

Assistant Commissioner of Patents.

Certificate of Correction Patent No. 2,510,707 June 6, 1950 DAVID L. MARKUSEN It is hereby certied that error appears in the printed speciflcation of the above numbered patent requiring correction as follows:

Column 2, line 31, for directly read indirectly; column 10, lines 60 and 61, strike out over a range of values and insert the same in line 59, after the Word magnitude and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oflce.

, Signed and sealed this 31st day of October, A. D. 1950.

[SML] THOMAS F. MURPHY,

Assistant ommz'ssz'oner of Patents. 

